Photocatalyst transfer film and production method thereof

ABSTRACT

Provided are a photocatalyst transfer film allowing a uniform and highly transparent photocatalyst layer to be transferred to the surfaces of various transfer base materials; and a production method thereof. The photocatalyst transfer film has, on a biaxially oriented polypropylene film, a photocatalyst layer containing a titanium oxide particle-containing photocatalyst, a silicon compound and a surfactant. The production method of the photocatalyst transfer film includes applying a photocatalyst coating liquid to a biaxially oriented polypropylene film; and performing drying. The photocatalyst coating liquid contains a titanium oxide particle-containing photocatalyst, a silicon compound, a surfactant and an aqueous dispersion medium.

TECHNICAL FIELD

The present invention relates to a transfer film used to produce a base material having a photocatalyst on its surface; and a production method thereof.

BACKGROUND ART

A photocatalyst film laminated on the surface of a base material has been utilized for purposes such as cleaning, deodorizing and causing an antimicrobial effect on the base material surface, because a photocatalytic metal compound contained in the photocatalyst film, such as titanium oxide, is capable of decomposing organic substances when irradiated with an ultraviolet light-visible light and thus exhibiting a hydrophilic property.

In recent years, photocatalyst materials have gained attention as inorganic antimicrobial-antifungal agents, and are now gradually being put to practical use for purposes such as cleaning, deodorizing and causing an antimicrobial effect on base material surfaces. The photocatalytic reaction is a reaction caused by excited electrons and holes occurring as a result of a photocatalytic metal compound such as titanium oxide absorbing lights. The mechanism for acting as an antimicrobial agent is assumed as such that the excited electrons and holes that have been generated on the surface of a photocatalytic metal compound by the photocatalytic reaction will contribute to an oxidation-reduction reaction with the oxygen and water adsorbed to the surface of the photocatalytic metal compound, an active species thus generated will then act on microorganisms to annihilate them by causing damages to the cell membranes thereof, or even eventually decompose those microorganisms by acting on them for a long period of time. Thus, it can be said that the benefits of a photocatalyst material include, for example, the fact that it is effective on a wide variety of organisms such as fungi and also less likely to produce resistant bacteria, and the fact that the material hardly deteriorates with time.

As a method for producing a base material having a photocatalyst, there is employed a method where a photocatalyst-containing coating liquid is to be directly applied to the surface of a base material via a coating method such as a spray coating method, a roll coating method and a brush coating method, followed by performing drying. However, this method has exhibited a problem of lacking productivity.

Meanwhile, although a transfer method using a transfer sheet or film with a photocatalyst layer already being formed thereon is superior in productivity, the method has a problem that a film cannot be formed in a uniform manner; and a problem that a mold release property will be impaired as residues of the transfer sheet may remain on the base material after transfer.

JP-A-2001-260597 (Patent document 1) discloses a transfer film with a photocatalyst layer, an inorganic protective layer and an organic adhesive layer being integrally laminated on a base film. Further, WO01/025362 (Patent document 2) discloses a transfer film or sheet with a photocatalyst layer and an adhesive layer being laminated on the surface of a film-shaped or sheet-shaped base material.

However, in order to improve a transferability, these transfer sheets or films are required to have a laminated structure composed of at least three layers, which has led to a problem that the productivity of these transfer sheets or films is poor.

As a photocatalyst film for transfer, there is desired a photocatalyst film that is superior in productivity; and is capable of being easily subjected to transfer processing, capable of being transferred while maintaining a photocatalytic function, and capable of exhibiting an excellent design property as being highly transparent even after transfer.

As a photocatalyst, since it is required that only a small degree of change in appearance be observed after forming a film on the base material, it is desired that there be used a photocatalyst dispersion liquid with a high transparency. JP-A-2005-131552 (Patent document 3) discloses a transfer sheet comprised of a transparent photocatalyst layer-forming composition. Here, while it is difficult to apply such photocatalyst coating liquid as a highly transparent aqueous dispersion to an organic film due to the influence of a surface tension, it is also conceivable to lower the surface tension of the liquid by mixing a solvent thereinto before performing coating. However, the problem is that transparency may be impaired as photocatalyst particles may be precipitated depending on the type of the solvent, or that it is difficult to form a uniform film in actual production steps as the coating film may contract in the midst of a drying procedure due to differences in evaporation rates in the mixed liquid.

In order to obtain a stable film transferred, a primer layer is known to be provided on a transfer film. However, this makes the production process of the film cumbersome, and thus causes the problem of lacking productivity. Further, processing at a high temperature is required. Moreover, although an inexpensive PET film is preferred as a base film, the PET film has the following problems. That is, when using a PET film as the base film, the transfer of the base film component will occur as mold releasing will take place in an insufficient manner at the time of transfer processing, thereby causing organic substances derived from the base film to remain on the surface of a base material after transfer, thus inhibiting the photocatalytic function. Also, in the case of a photocatalyst transfer film, the usage of an inexpensive base film is required as the base film will be discarded after transfer.

While a mold release film may also be used to improve a mold releasability from the base film, a problem with such mold release film is that when applying a low-viscosity solution such as a photocatalyst dispersion liquid not containing a resin(s) as a binder, it will be difficult to form a stable film as coating unevenness will occur easily.

Meanwhile, while a film forming capability may be improved by mixing an organic resin binder component(s) into a photocatalyst, there exists a problem that a photocatalytic activity will be impaired as the organic resin binder component(s) will cover the photocatalyst particles. Further, in order to make transfer processing easier, there may be used a type of film with a silicone layer being provided on the mold release film, and a photocatalyst layer being further provided thereon. However, a problem with this type of film is, for example, such that an insufficient photocatalytic activity will be achieved as a resin layer comprised of a small amount of silicone or the like will cover the surface after transfer.

PRIOR ART DOCUMENTS Patent Documents

Patent document 1: JP-A-2001-260597

Patent document 2: WO01/025362

Patent document 3: JP-A-2005-131552

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

Therefore, it is an object of the present invention to provide a photocatalyst transfer film superior in productivity, capable of yielding a photocatalyst thin film with a high transparency, and having a favorable molding processability; and a production method thereof.

Means to Solve the Problems

The inventors of the present invention diligently conducted a series of studies to solve the above problems, and completed the invention as follows. That is, the inventors found that a uniform and highly transparent photocatalyst film can be easily formed on the surfaces of various base materials by using a photocatalyst transfer film with a photocatalyst-, silicon compound- and surfactant-containing photocatalyst layer being laminated on a biaxially oriented polypropylene film.

Thus, the present invention is to provide the following photocatalyst transfer film and a production method thereof.

[1]

A photocatalyst transfer film having, on a biaxially oriented polypropylene film, a photocatalyst layer containing a titanium oxide particle-containing photocatalyst, a silicon compound and a surfactant.

[2]

The photocatalyst transfer film according to [1], wherein the silicon compound is a hydrolysis condensate of a tetrafunctional silicon compound, the hydrolysis condensate being obtained under the presence of an organic ammonium salt.

[3]

The photocatalyst transfer film according to [1] or [2], wherein the surfactant is an acetylene-based surfactant.

[4]

The photocatalyst transfer film according to any one of [1] to [3], wherein the photocatalyst layer has a thickness of 20 to 300 nm.

[5]

The photocatalyst transfer film according to any one of [1] to [4], wherein the biaxially oriented polypropylene film has a thickness of 12.5 to 100 μm.

[6]

The photocatalyst transfer film according to any one of [1] to [5], wherein a protective layer containing a silicon compound is further laminated on the photocatalyst layer.

[7]

A method for producing a photocatalyst transfer film, comprising:

applying a photocatalyst coating liquid to a biaxially oriented polypropylene film, the photocatalyst coating liquid containing a titanium oxide particle-containing photocatalyst, a silicon compound, a surfactant and an aqueous dispersion medium; and

performing drying.

Effects of the Invention

According to the present invention, provided are a photocatalyst transfer film allowing a uniform and highly transparent photocatalyst film to be transferred to the surfaces of various base materials by transfer processing; and a production method thereof. Further, the photocatalyst transfer film of the present invention is also superior in productivity.

MODE FOR CARRYING OUT THE INVENTION

Described hereunder are a photocatalyst transfer film of the present invention and a method for producing the same.

Photocatalyst Transfer Film Base Film

A base film used in the photocatalyst transfer film of the present invention is a biaxially oriented polypropylene (OPP) film, and a film that has not yet been subjected to a surface treatment is preferred in terms of outer appearance and photocatalytic effect after transfer processing. Here, the biaxially oriented polypropylene film refers to a film that has been drawn by a known manufacturing process and has a high amount of oriented crystals.

Further, it is preferred that the biaxially oriented polypropylene film have an arithmetic average roughness Ra of 0.01 to 1 μm, more preferably 0.05 to 0.8 μm, when measured by a 3D laser microscope. It is not preferable when the Ra value of the biaxially oriented polypropylene film is smaller than 0.01 μm, because it will be difficult to produce a uniform film. Meanwhile, an Ra value of not larger than 1 μm is preferred in terms of photocatalytic effect after transfer.

Photocatalyst Layer

A photocatalyst layer of the photocatalyst transfer film of the present invention contains a titanium oxide particle-containing photocatalyst, a silicon compound and a surfactant. Such photocatalyst layer can be formed by performing coating with a photocatalyst coating liquid containing a titanium oxide particle-containing photocatalyst, a silicon compound, a surfactant and an aqueous dispersion medium.

Titanium Oxide Particle-Containing Photocatalyst

As for the photocatalyst of the present invention, it is preferred that there be used a photocatalyst superior in transparency in view of design features after processing.

In this specification, the term “photocatalyst” is a collective term referring to a substance exhibiting a photocatalytic action when irradiated with a light having an energy not lower than a given bandgap. Examples of such substance include known metal oxide semiconductors such as titanium oxide, tungsten oxide, zinc oxide, tin oxide, iron oxide, bismuth oxide, bismuth vanadate and strontium titanate. As the photocatalyst used in the photocatalyst transfer film of the present invention, particles of any one kind of these substances may be used, or particles of two or more kinds of these substances may be used in combination. Particularly, it is preferred that there be used titanium oxide particles having an especially high photocatalytic action when irradiated with a light beam containing an ultraviolet light of a wavelength of not higher than 400 nm (preferably 280 to 380 nm), being chemically stable, allowing nanosized particles to be synthesized relatively easily, and being able to be relatively easily dispersed in a solvent of such nanosized particles.

As crystalline phases of titanium oxide particles, there are generally known three of them which are the rutile-type, anatase-type and brookite-type. It is preferred that there be used titanium oxide particles mainly composed of the anatase-type or rutile-type. Here, the expression “mainly composed” refers to an occupancy of usually not smaller than 50% by mass, preferably not smaller than 70% by mass, even more preferably not smaller than 90% by mass, or even 100% by mass in all the crystals of the titanium oxide particles.

As titanium oxide particles, there may be employed those with metal compounds of platinum, gold, palladium, iron, copper, nickel or the like being supported on titanium oxide particles, and those doped with elements such as tin, nitrogen, sulfur and carbon, for the purpose of improving the photocatalytic activity of the particles. It is preferred that there be used titanium oxide particles doped with the above elements as particle size control will be easy, and a film superior in transparency will be able to be obtained.

In terms of transparency after coating, it is preferred that a titanium oxide particle dispersion liquid be used as the photocatalyst coating liquid for forming the photocatalyst layer. As the aqueous dispersion medium for the titanium oxide particle dispersion liquid, an aqueous solvent is normally used, and it is preferred that there be used water, a water-soluble organic solvent mixable with water, and a mixed solvent prepared by mixing water and a water-soluble organic solvent at any ratio. As water, preferred are, for example, a deionized water, a distilled water and a pure water. Moreover, as the water-soluble organic solvent, preferred are, for example, alcohols such as methanol, ethanol and isopropanol; glycols such as ethylene glycol; and glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether and propylene glycol-n-propyl ether. As the aqueous dispersion medium, any one kind of them may be used alone, or two or more kinds of them may be used in combination. If using the mixed solvent, it is preferred that a ratio between the water-soluble organic solvent and water be 1/10 to 15/10.

It is preferred that the titanium oxide particle dispersion liquid be that bringing about a high transparency after film formation, and it is preferred that the titanium oxide particles be fine particles. As for a dispersed particle size of such particles, a 50% cumulative distribution diameter D₅₀ on volume basis that is measured by a dynamic light scattering method using a laser light (possibly referred to as “average particle size” hereunder) is preferably 5 to 30 nm, more preferably 5 to 20 nm. This is because when the average particle size is smaller than 5 nm, an insufficient photocatalytic activity may be exhibited; and when the average particle size is greater than 30 nm, the dispersion liquid may turn non-transparent. Here, as a device for measuring the average particle size, there may be used, for example, ELSZ-2000ZS (by Otsuka Electronics Co., Ltd.), NANOTRAC UPA-EX150 (by Nikkiso Co., Ltd.), and LA-910 (by HORIBA, Ltd.).

It is preferred that the concentration of the titanium oxide particles in the titanium oxide particle dispersion liquid be 0.01 to 30% by mass, particularly preferably 0.5 to 20% by mass, in terms of ease in producing a later-described photocatalyst thin film having a given thickness.

Here, a method for measuring the concentration of the titanium oxide particle dispersion liquid may be such that part of the titanium oxide particle dispersion liquid is taken as a sample, followed by heating it at 105° C. for three hours so as to volatilize the solvent, and then calculating the concentration in accordance with the following formula based on the mass of the non-volatile content (titanium oxide particles), and the mass of the sampled titanium oxide particle dispersion liquid before heating.

Concentration of titanium oxide particle dispersion liquid (% by mass)=[mass of non-volatile content (g)/mass of titanium oxide particle dispersion liquid before heating (g)]×100

Silicon Compound

The silicon compound contained in the photocatalyst layer of the photocatalyst transfer film of the present invention is used as a binder in the photocatalyst layer.

Here, a “silicon compound-based binder” refers to a colloid dispersion, solution or emulsion of a silicon compound that is provided in a way such that a solid or liquid silicon compound is contained in an aqueous dispersion medium. Specific examples of such silicon compound-based binder include a colloidal silica (preferable average particle size 1 to 150 nm); solutions of silicates; silane, siloxane hydrolysate emulsions; silicone resin emulsions; and emulsions of copolymers of silicone resins and other resins, such as a silicone-acrylic resin copolymer and a silicone-urethane resin copolymer. Particularly, it is preferred that there be used a solution of silicates that is obtained by hydrolytic condensation of a tetrafunctional silicon compound under the presence of a basic compound. Examples of the tetrafunctional silicon compound include amorphous silica, silicon tetrachloride, tetraethoxysilane and tetramethoxysilane. Further, it is preferred that the basic compound be an organic ammonium salt, specific and preferable examples of which include tetramethylammonium hydroxide, triethylammonium hydroxide, tetrabutylammonium hydroxide and ethyltrimethylammonium hydroxide. The hydrolytic condensation reaction of the tetrafunctional silicon compound is performed in an aqueous medium and under the presence of a basic compound at a temperature of normal temperature to 170° C., using, as a raw material, the tetrafunctional silicon compound in an amount of preferably 1 to 20% by mass, more preferably 1 to 15% by mass with respect to a reaction system (raw material mixed liquid). It is preferred that the basic compound be added in an amount of not smaller than 100 mol %, more preferably 100 to 500 mol %, with respect to the tetrafunctional silicon compound.

When the tetrafunctional silicon compound is silica, it is preferable to prepare a raw material mixed liquid having a SiO₂ concentration of 1 to 15% by mass, a basic compound concentration of 2 to 25% by mass and water as a remainder, and then heat and stir such mixed liquid at 80 to 130° C.

Surfactant

Examples of the surfactant contained in the photocatalyst layer of the photocatalyst transfer film of the present invention include anionic surfactants such as fatty acid sodium salt, alkylbenzene sulfonate, higher alcohol sulfate ester salt and polyoxyethylene alkyl ether sulfate salt; cationic surfactants such as alkyltrimethyl ammonium salt, dialkyldimethyl ammonium salt, alkyldimethylbenzyl ammonium salt and quaternary ammonium salt; amphoteric surfactants such as alkylamino fatty acid salt, alkyl betaine and alkylamine oxide; and non-ionic surfactants such as polyoxyethylene alkyl ether, polyoxyethylene alkylphenol ether, alkyl glucoside, polyoxyethylene fatty acid ester, sucrose fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, fatty acid alkanolamide and an acetylene-based surfactant. Among these examples, non-ionic surfactants are preferred in terms of stability of the coating liquid.

Further, a surfactant with an HLB value of 7 to 18 is preferred, and a surfactant with an HLB value of 10 to 15 is even more preferred. Particularly, an acetylene-based surfactant is preferred in terms of dispersibility, and a surfactant represented by the following general formula is more preferred.

R¹—C≡C—R²

Each of R¹ and R² independently represents a monovalent organic group, preferably a hydrocarbon group with part of its hydrogen atoms being substituted by an OH group(s), and having 1 to 20 carbon atoms. Moreover, each of R¹ and R² may also be a hydrocarbon group having 1 to 20 carbon atoms, but with part of the hydrocarbon group having an ether bond(s). Examples of an acetylene-based surfactant include OLFINE EXP4001, EXP4200, EXP4123 and EXP4300 (by Nissin Chemical Industry Co., Ltd.).

Method for Preparing Photocatalyst Coating Liquid

The photocatalyst coating liquid for forming the photocatalyst layer of the photocatalyst transfer film of the present invention can be prepared by adding a silicon compound and a surfactant to the photocatalyst containing the titanium oxide particles.

In the beginning, as the photocatalyst containing the titanium oxide particles, the titanium oxide particle dispersion liquid can be produced by a method including the following steps (1) and (2).

(1) Step of producing a peroxotitanic acid solution from a raw material titanium compound, a basic substance, hydrogen peroxide and an aqueous dispersion medium. (2) Step of obtaining the titanium oxide particle dispersion liquid by heating the peroxotitanic acid solution produced in the step (1) at 80 to 250° C. under a controlled pressure.

Each step is described in detail hereunder.

Step (1)

In the step (1), the peroxotitanic acid solution is produced by reacting the raw material titanium compound, the basic substance and hydrogen peroxide in the aqueous dispersion medium.

As a method for producing the peroxotitanic acid solution, there may be employed a method where the basic substance is added to the raw material titanium compound in the aqueous dispersion medium to obtain titanium hydroxide, followed by eliminating impurity ions other than the metal ions contained, and then adding hydrogen peroxide thereto so as to obtain peroxotitanic acid; or a method where after adding hydrogen peroxide to the raw material titanium compound, the basic substance is then added thereto to obtain a peroxotitanium hydrate, followed by eliminating impurities other than the metal ions contained, and then further adding hydrogen peroxide thereto so as to obtain peroxotitanic acid.

Here, examples of the raw material titanium compound include titanium chlorides; inorganic acid salts such as nitrates and sulfates; organic acid salts such as formic acid, citric acid, oxalic acid, lactic acid and glycolic acid; and titanium hydroxides precipitated as a result of performing hydrolysis by adding alkalis to the aqueous solutions of these compounds. Any one of them may be used alone, or two or more of them may be used in combination. Particularly, as the raw material titanium compound, it is preferred that a titanium chloride(s) (TiCl₃, TiCl₄) be used.

As the aqueous dispersion medium, an aqueous dispersion medium similar to that in the titanium oxide particle dispersion liquid is used such that the aforementioned composition will be achieved. Here, the concentration of the raw material titanium compound aqueous solution comprised of the raw material titanium compound and the aqueous dispersion medium is not higher than 60% by mass, particularly preferably not higher than 30% by mass. While the lower limit of such concentration may be appropriately selected, it is preferred that the concentration be not lower than 1% by mass in general.

The basic substance is used to smoothly turn the raw material titanium compound into titanium hydroxide; examples of such basic substance include hydroxides of alkali metals or alkali earth metals, such as sodium hydroxide and potassium hydroxide; and amine compounds such as ammonia, alkanolamine and alkylamine. The basic substance is added in an amount at which the raw material titanium compound aqueous solution will have a pH level of not lower than 7, particularly 7 to 10. Here, the basic substance may also be used in the form of an aqueous solution having an appropriate concentration when combined with the aqueous dispersion medium.

Hydrogen peroxide is used to convert the raw material titanium compound or titanium hydroxide into peroxotitanium i.e. a titanium oxide compound containing a Ti—O—O—Ti bond, and is normally used in the form of a hydrogen peroxide water. It is preferred that hydrogen peroxide be added in an amount of 1.5 to 20 times larger than the substance quantity of titanium in terms of mole. Further, in the reaction where hydrogen peroxide is added to turn the raw material titanium compound or titanium hydroxide into peroxotitanic acid, it is preferred that a reaction temperature be 5 to 80° C., and that a reaction time be 30 min to 24 hours.

The peroxotitanic acid solution thus obtained may also contain an alkaline substance or an acidic substance for the purpose of pH adjustment or other purposes. Here, examples of the alkaline substance include ammonia, sodium hydroxide, calcium hydroxide and alkylamine. Examples of the acidic substance include inorganic acids such as sulfuric acid, nitric acid, hydrochloric acid, carbonic acid, phosphoric acid and hydrogen peroxide; and organic acids such as formic acid, citric acid, oxalic acid, lactic acid and glycolic acid. In this case, it is preferred that the peroxotitanic acid solution obtained have a pH level of 1 to 9, particularly preferably 4 to 7 in terms of safety in handling.

Step (2)

In the step (2), the peroxotitanic acid solution obtained in the step (1) is subjected to a hydrothermal reaction at a temperature of 80 to 250° C., preferably 100 to 250° C. for 0.01 to 24 hours under a controlled pressure. An appropriate reaction temperature is 80 to 250° C. in terms of reaction efficiency and reaction controllability; as a result, the peroxotitanic acid will be converted into titanium oxide particles. Here, the expression “under a controlled pressure” refers to a state where when the reaction temperature employed is greater than the boiling point of the dispersion medium, pressure will be applied in an appropriate manner such that the reaction temperature can be maintained; as well as a state where when the reaction temperature employed is not higher than the boiling point of the dispersion medium, atmospheric pressure will be used for control. Here, the pressure is normally about 0.12 to 4.5 MPa, preferably about 0.15 to 4.5 MPa, more preferably 0.20 to 4.5 MPa. The reaction time is preferably 1 min to 24 hours. The titanium oxide particle dispersion liquid is obtained via this step (2).

While it is preferred that the particle size of the titanium oxide particles thus obtained be within the aforementioned range(s), the particle size can be controlled by adjusting the reaction conditions. For example, the particle size can be reduced by shortening the reaction time and a heatup time.

Next, a silicon compound is added to the titanium oxide particle dispersion liquid prepared above in a way such that a mass ratio of silicon compound:titanium oxide particle will preferably be 1:99 to 99:1, more preferably 10:90 to 90:10, even more preferably 30:70 to 70:30.

Next, the silicon compound-containing titanium oxide particle dispersion liquid is diluted with an aqueous dispersion medium in a way such that a concentration of the titanium oxide and the silicon compound will be 0.1 to 10% by mass, preferably 0.3 to 5% by mass.

As the aqueous dispersion medium, it is preferred that there be used water, a water-soluble organic solvent mixable with water, and a mixed solvent prepared by mixing water and a water-soluble organic solvent at any ratio. As water, preferred are, for example, a deionized water, a distilled water and a pure water. Moreover, as the water-soluble organic solvent, preferred are, for example, alcohols such as methanol, ethanol and isopropanol; glycols such as ethylene glycol; and glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether and propylene glycol-n-propyl ether. Alcohols are particularly preferred as a stable dispersibility will be achieved easily. It is preferred that a weight ratio of the water-soluble organic solvent/water in the mixed solvent be larger than 1/10, but not larger than 15/10; more preferably larger than 2/10, but not larger than 12/10.

A surfactant is then added to the silicon compound-containing titanium oxide particle dispersion liquid that has been diluted, at a ratio of 0.001 to 5% by mass, preferably 0.01 to 1% by mass, in terms of liquid weight ratio, thereby obtaining the photocatalyst coating liquid.

In the present invention, a small amount of a metal component(s) other than the titanium oxide particles may also be contained. For example, the photocatalyst layer may contain at least one kind of antimicrobial metal component in order to improve an antimicrobial-antifungal property of the photocatalyst layer.

The term “antimicrobial metal” refers to metals that are harmful to microorganisms such as bacteria and fungi (molds), but are relatively less harmful to the human body; examples of such metals include silver, copper, zinc, platinum, palladium, nickel, aluminum, titanium, cobalt, zirconium, molybdenum and tungsten.

The photocatalyst layer of the photocatalyst transfer film of the present invention may also contain alloy particles containing at least one kind of metal selected from these antimicrobial metals.

More specifically, there may be used alloy particles comprised of combinations of metals, such as silver-copper, silver-palladium, silver-platinum, silver-tin, gold-copper, silver-nickel, silver-antimony, silver-copper-tin, gold-copper-tin, silver-nickel-tin, silver-antimony-tin, platinum-manganese, silver-titanium, copper-tin, cobalt-copper, zinc-magnesium, silver-zinc, copper-zinc and silver-copper-zinc.

In addition, there are no particular restrictions on the components in the alloy particles other than the antimicrobial metal(s); examples of such components may include gold, antimony, tin, sodium, magnesium, silicon, phosphorus, sulfur, potassium, calcium, scandium, vanadium, chromium, manganese, iron, gallium, germanium, arsenic, selenium, yttrium, niobium, technetium, ruthenium, rhodium, indium, tellurium, cesium, barium, hafnium, tantalum, rhenium, osmium, iridium, mercury, thallium, lead, bismuth, polonium, radium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, actinium and thorium. Any one of them may be used alone, or two or more of them may be used in combination.

The antimicrobial metal(s) in the alloy particles are contained in an amount of 1 to 100% by mass, preferably 10 to 100% by mass, more preferably 50 to 100% by mass, with respect to the total mass of the alloy particles. This is because when the antimicrobial metal(s) are in an amount of smaller than 1% by mass with respect to the total mass of the alloy particles, an insufficient antimicrobial-antifungal capability may be exhibited.

If the photocatalyst layer of the photocatalyst transfer film of the present invention is to contain alloy particles comprised of antimicrobial metals, it is preferred that an alloy particle dispersion liquid be used as the photocatalyst coating liquid for forming the photocatalyst layer. As the aqueous dispersion medium for the alloy particle dispersion liquid, an aqueous solvent is normally used; preferred are water, a water-soluble organic solvent mixable with water, and a mixed solvent prepared by mixing water and a water-soluble organic solvent at any ratio. As water, preferred are, for example, a deionized water, a distilled water and a pure water. Further, examples of the water-soluble organic solvent include alcohols such as methanol, ethanol, n-propanol, 2-propanol, n-butanol, 2-butanol, tert-butanol, ethylene glycol, diethylene glycol and polyethylene glycol; glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether and propylene glycol-n-propyl ether; ketones such as acetone and methyl ethyl ketone; water-soluble nitrogen-containing compounds such as 2-pyrrolidone and N-methylpyrrolidone; and ethyl acetate. Any one of them may be used alone, or two or more of them may be used in combination.

It is preferred that the alloy particles in the alloy particle dispersion liquid be fine particles, and as for a dispersed particle size thereof, a 50% cumulative distribution diameter D₅₀ on volume basis that is measured by a dynamic light scattering method using a laser light (possibly referred to as “average particle size” hereunder) is preferably not larger than 200 nm, more preferably not larger than 100 nm, even more preferably not larger than 70 nm. There are no particular restrictions on the lower limit of the average particle size, and theoretically, even those having the minimum particle size enabling antimicrobial-antifungal property may be used. However, practically, it is preferred that the average particle size be not smaller than 1 nm. Further, it is not preferable when the average particle size is greater than 200 nm, because the dispersion liquid may turn non-transparent. Here, as a device for measuring the average particle size, there may be used, for example, ELSZ-2000ZS (by Otsuka Electronics Co., Ltd.), NANOTRAC UPA-EX150 (by Nikkiso Co., Ltd.), and LA-910 (by HORIBA, Ltd.).

There are no particular restrictions on the concentration of the alloy particles in the alloy particle dispersion liquid. However, in general, the lower the concentration is, the better the dispersion stability becomes. Thus, it is preferred that the concentration be 0.0001 to 10% by mass, more preferably 0.001 to 5% by mass, even more preferably 0.01 to 1% by mass. It is not preferable when the concentration is lower than 0.0001% by mass, because the productivity of the photocatalyst transfer film will decrease in a significant manner.

If the photocatalyst layer of the photocatalyst transfer film of the present invention is to contain alloy particles comprised of antimicrobial metals, it is preferred that the photocatalyst coating liquid be produced by, as described above, adding a silicon compound and a surfactant to a mixed dispersion liquid that has been prepared by previously mixing two kinds of particle dispersion liquids which are the titanium oxide particle dispersion liquid and the alloy particle dispersion liquid containing antimicrobial metals; the titanium oxide particle dispersion liquid and the alloy particle dispersion liquid are prepared separately.

Specifically, there may be employed a method where the alloy dispersion liquid is produced by the following steps (3) to (5), and the titanium oxide particle dispersion liquid and the alloy particle dispersion liquid are then mixed together by the following step (6).

(3) Step of producing a solution containing a raw material antimicrobial metal compound, and a solution containing a reductant for reducing such metal compound.

(4) Step of producing an alloy particle dispersion liquid by mixing the solutions produced in the step (3) which are the solution containing the raw material antimicrobial metal compound, and the solution containing the reductant for reducing such metal compound.

(5) Step of washing the alloy particle dispersion liquid produced in the step (4) with an aqueous dispersion medium by a membrane filtration method.

(6) Step of mixing the titanium oxide particle dispersion liquid obtained in the step (2) and the alloy particle dispersion liquid obtained in the step (5).

The steps (3) to (5) are steps for producing the alloy particle dispersion liquid. While there are various physical and chemical methods, these production steps particularly employ a liquid phase reduction method which is a chemical method having advantages in terms of ease in adjusting synthesis conditions, wider controllable ranges of, for example, composition, particle size and particle size distribution, and productivity of the alloy particles. In such liquid phase reduction method, alloy particles are to be precipitated by mixing a reductant into a solution containing at least two kinds of metal ions serving as alloy raw materials. At that time, by allowing a protective agent of the alloy particles to coexist in the reaction system, the dispersibility of the alloy particles in the solvent can also be further improved.

The step (6) is a step for finally producing the titanium oxide-alloy particle mixed dispersion liquid, by mixing the titanium oxide particle dispersion liquid obtained in the step (2) and the alloy particle dispersion liquid obtained in the step (5).

Each step is described in detail hereunder.

Step (3)

In the step (3), produced are the solution with the raw material antimicrobial metal compound being dissolved in an aqueous dispersion medium; and the solution with the reductant for reducing such raw material antimicrobial metal compound being dissolved in an aqueous dispersion medium.

As a method for producing these solutions, there may be employed a method where the raw material antimicrobial metal compound and the reductant for reducing such raw material antimicrobial metal compound are individually and separately added to an aqueous dispersion medium, followed by performing stirring so as to allow them to be dissolved therein. There are no particular restrictions on a stirring method as long as the method employed enables a uniform dissolution in the aqueous dispersion medium; a commonly available stirrer can be used.

Various antimicrobial metal compounds may be used as the raw material antimicrobial metal compound, examples of which include antimicrobial metal chlorides; inorganic acid salts such as nitrates and sulfates; organic acid salts such as formic acid, citric acid, oxalic acid, lactic acid and glycolic acid; and complex salts such as amine complex, cyano complex, halogeno complex and hydroxy complex. Any one of them may be used alone, or two or more of them may be used in combination. Particularly, it is preferred that chlorides and inorganic acid salts such as nitrates and sulfates be used.

There are no particular restrictions on the reductant; there can be used any kind of reductant capable of reducing the metal ions composing the raw material antimicrobial metal compound. Examples of the reductant include hydrazines such as hydrazine, hydrazine monohydrate, phenylhydrazine and hydrazinium sulfate; amines such as dimethylaminoethanol, triethylamine, octylamine and dimethylaminoborane; organic acids such as citric acid, ascorbic acid, tartaric acid, malic acid, malonic acid and formic acid; alcohols such as methanol, ethanol, isopropyl alcohol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol and benzotriazole; hydrides such as sodium borohydride, lithium borohydride, lithium triethylborohydride, lithium aluminum hydride, diisobutylaluminum hydride, tributyltin hydride, lithium tri(sec-butyl)borohydride, potassium tri(sec-butyl)borohydride, zinc borohydride and acetoxy sodium borohydride; pyrrolidones such as polyvinylpyrrolidone, 1-vinylpyrrolidone, N-vinylpyrrolidone and methylpyrrolidone; reducing sugars such as glucose, galactose, mannose, fructose, sucrose, maltose, raffinose and stachyose; and sugar alcohols such as sorbitol.

A protective agent may also be added to the solution with the reductant being dissolved in the aqueous dispersion medium. There are no particular restrictions on the protective agent as long as the protective agent employed is capable of preventing the alloy particles precipitated by reduction from agglutinating; there may be used a surfactant or an organic compound having a capability as a dispersant. Specific examples of the protective agent include surfactants such as anionic surfactants, cationic surfactants and nonionic surfactants; water-soluble polymer compounds such as polyvinylpyrrolidone, polyvinyl alcohol, polyethyleneimine, polyethylene oxide, polyacrylic acid and methylcellulose; aliphatic amine compounds such as ethanolamine, diethanolamine, triethanolamine and propanolamine; primary amine compounds such as butylamine, dibutylamine, hexylamine, cyclohexylamine, heptylamine, 3-butoxypropylamine, octylamine, nonylamine, decylamine, dodecylamine, hexadecylamine, oleylamine and octadecylamine; diamine compounds such as N,N-dimethylethylenediamine and N,N-diethylethylenediamine; and carboxylic acid compounds such as oleic acid.

As the aqueous dispersion medium (aqueous solvent), it is preferred that there be used water, a water-soluble organic solvent mixable with water, or a mixed solvent prepared by mixing water and a water-soluble organic solvent at any ratio. As water, preferred are, for example, a deionized water, a distilled water and a pure water. Further, examples of the water-soluble organic solvent include alcohols such as methanol, ethanol, isopropanol, n-propanol, 2-propanol, n-butanol, 2-butanol, tert-butanol, ethylene glycol and diethylene glycol; glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether and propylene glycol-n-propyl ether; ketones such as acetone and methyl ethyl ketone; water-soluble nitrogen-containing compounds such as 2-pyrrolidone and N-methylpyrrolidone; and ethyl acetate. As the aqueous dispersion medium, any one of them may be used alone, or two or more of them may be used in combination.

A basic substance or an acidic substance may be added to the aqueous dispersion medium. Examples of such basic substance include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; alkali metal carbonates such as sodium carbonate and potassium carbonate; alkali metal hydrogen carbonates such as sodium hydrogen carbonate and potassium hydrogen carbonate; alkali metal alkoxides such as potassium tert-butoxide, sodium methoxide and sodium ethoxide; alkali metal salts of aliphatic hydrocarbons such as butyl lithium; and amines such as triethylamine, diethylaminoethanol and diethylamine. Examples of the acidic substance include inorganic acids such as aqua regia, hydrochloric acid, nitric acid and sulfuric acid; and organic acids such as formic acid, acetic acid, chloroacetic acid, dichloroacetic acid, oxalic acid, trifluoroacetic acid and trichloroacetic acid.

There are no particular restrictions on the concentrations of the solution with the raw material antimicrobial metal compound being dissolved in the aqueous dispersion medium and the solution with the reductant for reducing such raw material antimicrobial metal compound being dissolved in the aqueous dispersion medium. However, there is a tendency that the lower these concentrations are, the smaller a primary particle size of each alloy particle formed will become. That is, it is preferred that a preferable concentration range(s) be determined based on the range of a target primary particle size.

There are no particular restrictions on the pH levels of the solution with the raw material antimicrobial metal compound being dissolved in the aqueous dispersion medium and the solution with the reductant for reducing such raw material antimicrobial metal compound being dissolved in the aqueous dispersion medium. It is preferred that the pH levels of these solutions be adjusted to preferable levels based on, for example, target molar ratios of the metals in the alloy particles and a target primary particle size.

Step (4)

In the step (4), the solution with the raw material antimicrobial metal compound being dissolved in the aqueous dispersion medium and the solution with the reductant for reducing such raw material antimicrobial metal compound being dissolved in the aqueous dispersion medium, which have been prepared in the step (3), are mixed to produce the alloy particle dispersion liquid.

There are no particular restrictions on a method for mixing these two solutions, as long as the method employed allows the two solutions to be uniformly mixed together. For example, there may be employed a method where the metal compound solution and the reductant solution are put into a reaction container before being stirred and mixed together; a method where stirring and mixing is performed in a way such that the reductant solution is delivered by drops into the metal compound solution already placed in a reaction container while stirring such metal compound solution; a method where stirring and mixing is performed in a way such that the metal compound solution is delivered by drops into the reductant solution already placed in a reaction container while stirring such reductant solution; or a method where the metal compound solution and the reductant solution are continuously supplied in constant amounts such that a reaction container or a microreactor, for example, may then be used to perform mixing.

There are no particular restrictions on a temperature at the time of preforming mixing; it is preferred that the temperature be adjusted to a preferable temperature based on, for example, target molar ratios of the metals in the alloy particles and a target primary particle size.

Step (5)

In the step (5), the alloy particle dispersion liquid produced in the step (4) is washed with an aqueous dispersion medium by a membrane filtration method.

As the aqueous dispersion medium, it is preferred that there be used water, a water-soluble organic solvent mixable with water, or a mixed solvent prepared by mixing water and a water-soluble organic solvent at any ratio. As water, preferred are, for example, a deionized water, a distilled water and a pure water. Further, examples of the water-soluble organic solvent include alcohols such as methanol, ethanol, isopropanol, n-propanol, 2-propanol, n-butanol, 2-butanol, tert-butanol, ethylene glycol and diethylene glycol; glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether and propylene glycol-n-propyl ether; ketones such as acetone and methyl ethyl ketone; water-soluble nitrogen-containing compounds such as 2-pyrrolidone and N-methylpyrrolidone; and ethyl acetate. As the water-soluble organic solvent, any one of them may be used alone, or two or more of them may be used in combination.

In the step (5), a membrane filtration method is used to wash and separate non-volatile impurities other than the alloy particles, such as components other than the metals in the raw material metal compound, the reductant and the protective agent, away from the alloy particle dispersion liquid produced in the step (4).

It is preferred that washing be performed repeatedly until a mass ratio between the alloy particles and the non-volatile impurities in the alloy particle dispersion liquid (alloy particles/non-volatile impurities) has reached 0.01 to 10, more preferably 0.05 to 5, even more preferably 0.1 to 1. It is not preferable when the mass ratio is lower than 0.01, because there will be a large amount of impurities with respect to the alloy particles so that an antimicrobial, antifungal and deodorant properties imparted may not be fully exhibited; it is also not preferable when the mass ratio is greater than 10, because the dispersion stability of the alloy particles may deteriorate.

Determination of Metal Component Concentration in Alloy Particle Dispersion Liquid (ICP-OES)

The metal component concentration in the alloy particle dispersion liquid can be measured by appropriately diluting the alloy particle dispersion liquid with a pure water, and then introducing the diluted liquid into an inductively coupled plasma optical emission spectrometer (product name “Agilent 5110 ICP-OES” by Agilent Technologies, Inc.)

Determination of Non-Volatile Impurities other than Metal Components in Alloy Particle Dispersion Liquid

Here, the concentration of the non-volatile impurities other than the metal components in the alloy particle dispersion liquid can be calculated by subtracting the metal component concentration determined by the above ICP-OES from a non-volatile content concentration that is calculated based on a mass of non-volatile contents (alloy particles+non-volatile impurities) observed after the solvent has been volatilized as a result of heating part of the alloy particle dispersion liquid as a sample at 105° C. for three hours, and a mass of the sampled alloy particle dispersion liquid before heating.

Non-volatile impurity concentration (%)=[mass of non-volatile content (g)/mass of alloy particle dispersion liquid before heating (g)]×100-metal component concentration in alloy particle dispersion liquid (%)

There are no particular restrictions on a membrane used in the membrane filtration method, as long as the membrane used is capable of separating the alloy particles and the non-volatile impurities other than the alloy particles from the alloy particle dispersion liquid. Examples of such membrane include a microfiltration membrane, an ultrafiltration membrane and a nanofiltration membrane. Among these membranes, filtration can be carried out using a membrane having a suitable pore size.

As a filtration method, there may also be employed any of, for example, centrifugal filtration, pressure filtration and cross-flow filtration.

As for the shape of the filtration membrane, there may be appropriately employed those of, for example, a hollow-fiber type, a spiral type, a tubular type or a flat membrane type.

There are no particular restrictions on the material of the filtration membrane, as long as the material employed has a durability against the alloy particle dispersion liquid. The material may be appropriately selected from, for example, organic films such as those made of polyethylene, tetrafluoroethylene, difluoroethylene, polypropylene, cellulose acetate, polyacrylonitrile, polyimide, polysulfone and polyether sulfone; and inorganic films such as those made of silica, alumina, zirconia and titania.

Specific examples of the abovementioned filtration membrane include microza (by Asahi Kasei Chemicals Corporation), Amicon Ultra (by Merck Millipore Corporation), Ultra filter (by Advantec Toyo Kaisha, Ltd.) and MEMBRALOX (by Nihon Pall Ltd.).

Step (6)

In the step (6), the titanium oxide particle dispersion liquid obtained in the step (2) and the alloy particle dispersion liquid obtained in the step (5) are mixed to produce the titanium oxide-alloy particle mixed dispersion liquid.

There are no particular restrictions on a mixing method, as long as the method employed allows the two kinds of dispersion liquids to be uniformly mixed together; for example, mixing may be carried out by performing stirring using a commonly available stirrer.

A mixing ratio between the titanium oxide particle dispersion liquid and the alloy particle dispersion liquid in the photocatalyst coating liquid is 1 to 100,000, preferably 10 to 10,000, even more preferably 20 to 1,000, in terms of a particle mass ratio between the titanium oxide particles and the alloy particles in each dispersion liquid (titanium oxide particles/alloy particles). It is not preferable when the mass ratio is lower than 1, because the photocatalytic capability will not be fully exhibited; it is also not preferable when the mass ratio is greater than 100,000, because the antimicrobial-antifungal capability will not be fully exhibited.

Protective Layer

In the case of the photocatalyst transfer film of the present invention, a protective layer formed of a silicon compound may be further provided on the photocatalyst layer. The silicon compound used in the protective layer may include those similar to the silicon compounds that are added to the photocatalyst layer as binders, specific examples of which include colloidal silica (preferable average particle size being 1 to 150 nm); solutions of silicates; silane, siloxane hydrolysate emulsions; silicone resin emulsions; and emulsions of copolymers of silicone resins and other resins, such as a silicone-acrylic resin copolymer and a silicone-urethane resin copolymer. Particularly, it is preferred that there be used a silicate solution prepared by hydrolytic condensation of a tetrafunctional silicon compound under the presence of a basic compound. Examples of such tetrafunctional silicon compound include amorphous silica, silicon tetrachloride, tetraethoxysilane and tetramethoxysilane. Further, it is preferred that the basic compound be an organic ammonium salt, specific examples of which include tetramethylammonium hydroxide, triethylammonium hydroxide, tetrabutylammonium hydroxide and ethyltrimethylammonium hydroxide.

Method for Producing Photocatalyst Transfer Film

In the present invention, a method for producing the photocatalyst transfer film is such that the abovementioned photocatalyst coating liquid is to be applied to an OPP film to form a film of the photocatalyst layer.

The photocatalyst coating liquid may be applied to the OPP film by a known method that has been technically established. Specifically, a film of the photocatalyst coating liquid is formed by utilizing a method such as a spray coating method, a wire bar method, a die coating method, a gravure coating method, a micro gravure coating method, an inkjet method, a spin coating method or a dip coating method, followed by drying the coating film at 70 to 150° C., preferably 80 to 120° C., for 5 min to 2 hours, thereby obtaining a flat and smooth photocatalyst transfer film.

The dried photocatalyst layer may have a thickness of 20 to 300 nm, preferably 40 to 150 nm. When the film thickness of the photocatalyst layer is smaller than 20 nm, the photocatalytic effect may be small. Further, when the film thickness of the photocatalyst layer is larger than 300 nm, the photocatalyst layer may not be able to remain as a film.

In addition, a silicon compound-containing protective layer may be further laminated on the photocatalyst layer; coating with a silicon compound as contained in an aqueous dispersion medium may be performed by a known method that has been technically established. Specifically, a film of the silicon compound is formed by utilizing a method such as a spray coating method, a wire bar method, a die coating method, a gravure coating method, a micro gravure coating method, an inkjet method, a spin coating method or a dip coating method, followed by drying the coating film at 70 to 150° C., preferably 80 to 130° C., thereby obtaining a flat and smooth photocatalyst transfer film with the silicon compound-containing protective layer being laminated on the outermost surface thereof.

The dried protective layer containing the silicon compound may have a thickness of 20 to 300 nm, preferably 40 to 150 nm. When the film thickness of the protective layer is smaller than 20 nm, the protective layer may not be able to fully function as a protective layer. Further, when the film thickness of the protective layer is larger than 300 nm, the protective layer may break easily such that it may not be able to remain as a film.

Method for Using Photocatalyst Transfer Film Base Material Having Photocatalyst on Surface

The photocatalyst transfer film of the present invention can be used to form photocatalyst films on the surfaces of various base materials. Here, there are no particular restrictions on the base materials; examples of such base materials may include organic materials and inorganic materials. These materials may have various shapes depending on their purposes and intended uses.

Examples of the organic materials include synthetic resin materials such as a vinyl chloride resin (PVC), polyethylene (PE), polypropylene (PP), polycarbonate (PC), an acrylic resin, polyacetal, a fluorine resin, a silicone resin, a ethylene-vinyl acetate copolymer (EVA), acrylonitrile-butadiene rubber (NBR), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyvinyl butyral (PVB), an ethylene-vinyl alcohol copolymer (EVOH), a polyimide resin, polyphenylene sulfide (PPS), polyetherimide (PEI), polyether ether imide (PEEI), polyether ether ketone (PEEK), a melamine resin, a phenolic resin and an acrylonitrile-butadiene-styrene (ABS) resin; natural materials such as natural rubbers; and semisynthetic materials of these synthetic resin materials and natural materials. These materials may already be processed into particular shapes and structures such as those of films, sheets or other molded products as well as laminated bodies.

Examples of the inorganic materials include non-metallic inorganic materials and metallic inorganic materials.

Examples of the non-metallic inorganic materials include glass, ceramics and stone materials. They may already be processed into various shapes such as those of tiles, glass products, mirrors, walls and design materials.

Examples of metallic inorganic materials include cast iron, steel, iron, iron alloys, aluminum, aluminum alloys, nickel, nickel alloys and zinc die-cast. They may already be plated with the above metallic inorganic materials or coated with the above organic materials, or even be used to plate the surfaces of the above organic materials or non-metallic inorganic materials.

Further, a primer layer such as a silicone-based primer layer and an amine-based primer layer may be laminated on the surface of the base material; the primer layer makes transfer processing easy.

Base materials having the photocatalyst on the surfaces thereof include a base material used as an interior architectural material, such as a wall material, a wall paper, a ceiling material, a floor material, tiles, bricks, a wooden board, a resin board, a metallic plate, a tatami mat, a bathroom material and a melamine board for use in architectural structures; a base material used as, for example, a wall material, a ceiling material, a floor material, a seat, a handrail or a hanging strap for use in an automobile, trains and the like; a material for household furniture and livingware-related products such as curtains, a blind, a rug, a partition board, a glass product, a mirror, a film, a desk, a chair, a bed and a storage rack; a material for home electric appliances such as an air cleaner, an air conditioner, a refrigerator, a laundry machine, a personal computer, a printer, a tablet, a touch panel and a telephone set; as well as a base material used in, for example, a signboard and a film.

Method for Laminating Photocatalyst Film on Base Material

While the photocatalyst transfer film of the present invention can be processed and thus transferred to the above base materials by a known method, a laminating method and a pressing method are preferred as they allow the photocatalyst layer to be transferred uniformly. Although depending on the properties of the transfer base material side, it is preferred that a processing temperature be 110 to 170° C., more preferably 120 to 160° C. When the processing temperature is lower than 110° C., the photocatalyst layer may not be able to be transferred to the transfer base material side. When the processing temperature is greater than 170° C., photocatalytic properties may not be achieved as the OPP film as the base film of the photocatalyst transfer film will be transferred to the transfer base material side and cover the surface of the photocatalyst layer.

Here, in the present invention, a protective film can be further formed on the surface of the photocatalyst layer formed on the OPP film, or on the surface of the protective layer.

There, while any film may be used as the protective film, the abovementioned OPP film may be used as the protective film.

A laminated body with such protective film being formed thereon can, for example, be easily transported when formed into the shape of a roll by a roller.

WORKING EXAMPLES

The present invention is described in detail hereunder with reference to working and comparative examples. However, the present invention is not limited to the following working examples.

(1) Measurement of Photocatalyst Layer Element (Elemental Analysis)

In order to confirm the transfer of the photocatalyst layer to the transfer base material side, each sample obtained in the following working and comparative examples was cut into a size of 5 cm×5 cm, followed by using an energy dispersive X-ray fluorescence analyzer (XRF, EDX-7000 by Shimadzu Corporation) to perform X-ray fluorescence analysis on both the Ti element and Si element that are present on the transfer base material after transfer and on the base film peeled away. As for each element, “∘” was given when the element was detected, whereas “-” was given when the element was not detected. The results thereof are shown in Table 1.

(2) Hydrophilicity Evaluation (Water Contact Angle Measurement)

In order to confirm the effect of the photocatalyst, each evaluation sample obtained in the following working and comparative examples was irradiated with an ultraviolet light, followed by using a contact angle meter (DM-501 by Kyowa Interface Science Co., Ltd.) to measure the water contact angle of each sample. The results thereof are shown in Table 1.

(3) Appearance (Transparency)

The appearance of each evaluation sample obtained in the following working and comparative examples was visually confirmed; “x” was given when white turbidity was confirmed due to ununiform transfer, whereas “∘” was given when transparency was confirmed to have been maintained. The results thereof are shown in Table 1.

Further, the appearance of the base film peeled away after transfer was visually confirmed; “x” was given when white turbidity had occurred due to transfer unevenness, whereas “∘” was given when transparency was confirmed to have been maintained. The results thereof are shown in Table 1. When transferability was poor, the photocatalyst layer will partially remain on the transfer film side such that transparency will disappear.

(4) Smoothness

An arithmetic average roughness Ra of the surface of the base film of the photocatalyst transfer film was measured by a 3D laser microscope (OLS-4000 by Nikon Corporation). Average values (n=3) are shown in Table 1.

(5) Average Particle Size D₅₀

An average particle size D₅₀ of the particles in the titanium oxide particle dispersion liquid, the alloy particle dispersion liquid as well as the mixture of the two kinds of particles which were the titanium oxide particles and the alloy particles, was calculated as a 50% cumulative distribution diameter on volume basis that was measured by a dynamic light scattering method using a laser light, and with the aid of ELSZ-2000ZS (by Otsuka Electronics Co., Ltd.).

Preparation of Silicon Compound-Containing Liquid

An amorphous silica, water and ethyltrimethylammonium hydroxide (20% by mass aqueous solution by SACHEM Japan Godo Kaisha) were mixed together in a way such that a ratio between silica and ethyltrimethylammonium hydroxide would be silica:ethyltrimethylammonium hydroxide=1:2 (molar ratio), and that a silica content in the system at the beginning of the reaction would be 5% by mass, followed by stirring them for two hours while performing heating at 110° C. The solution obtained was then diluted with water so that a solid content concentration would be 1% by mass, followed by using an ion-exchange resin (product name: DOWEX 50W-X8 by Dow Corning Corp.) to adjust the pH level to 7.0, thereby obtaining a silicon compound-containing liquid.

Preparation of Titanium Oxide Particle Dispersion Liquid A

After diluting a 36% by mass titanium chloride (IV) aqueous solution tenfold with a pure water, a 10% by mass ammonia water was then gradually added thereto to neutralize and hydrolyze the same, thereby obtaining a precipitate of titanium hydroxide. The precipitate-containing solution at that time had a pH level of 9. The precipitate obtained was then subjected to a deionization treatment where addition of pure water and decantation were performed repeatedly. A 35% by mass hydrogen peroxide water was then added to the deionized precipitate of titanium hydroxide in a manner such that a ratio of H₂O₂/Ti (molar ratio) would become 5, followed by stirring them at room temperature for 24 hours for sufficient reaction, thereby obtaining a yellow and transparent peroxotitanic acid solution (a).

The peroxotitanic acid solution (a) of an amount of 400 mL was put into a 500 mL autoclave to be hydrothermally processed for 90 min under a condition of 130° C., 0.5 MPa, followed by performing concentration control by adding a pure water thereto, thereby obtaining a titanium oxide particle dispersion liquid A (non-volatile content concentration 1.0% by mass, average particle size D₅₀ 12 nm).

Preparation of Titanium Oxide Particle Dispersion Liquid B

A yellow and transparent peroxotitanic acid solution (b) was obtained in a similar manner as the preparation of the titanium oxide particle dispersion liquid A, except that tin chloride (IV) was added to and dissolved into the 36% by mass titanium chloride (IV) aqueous solution in a way such that a ratio of Ti/Sn (molar ratio) would be 20.

The peroxotitanic acid solution (b) of an amount of 400 mL was put into a 500 mL autoclave to be hydrothermally processed for 90 min under a condition of 150° C., followed by performing concentration control by adding a pure water thereto, thereby obtaining a titanium oxide particle dispersion liquid B (non-volatile content concentration 1.0% by mass, average particle size D₅₀ 10 nm).

The crystalline phases of the titanium oxide particles in the titanium oxide particle dispersion liquids A and B obtained were identified by measuring the powder X-ray diffraction of a titanium oxide particle powders collected after drying each titanium oxide particle dispersion liquid at 105° C. for three hours, using a desktop X-ray diffraction device (product name “D2 PHASER” by Bruker AXS GmbH).

The crystalline phase of the titanium oxide in the titanium oxide particle dispersion liquid A was confirmed to be anatase-type; the crystalline phase of the titanium oxide in the titanium oxide particle dispersion liquid B was confirmed to be rutile-type.

Preparation of Silver-Copper Alloy Particle Dispersion Liquid

With ethylene glycol being used as a solvent, a raw material metal compound-containing solution (i) was produced by dissolving therein silver nitrate and copper nitrate trihydrate in a way such that a concentration as Ag would become 2.50 mmol/L, and a concentration as Cu would become 2.50 mmol/L.

A reductant-containing solution (ii) was obtained by mixing 55% by mass of ethylene glycol and 8% by mass of a pure water, as solvents; 2% by mass of potassium hydroxide as a basic substance; 20% by mass of hydrazine monohydrate and 5% by mass of dimethylaminoethanol, as reductants; and 10% by mass of polyvinylpyrrolidone as a reductant/protective agent.

A liquid obtained by rapidly mixing 2 L of the raw material metal compound-containing solution (i) heated to 160° C. in a reactor and 0.2 L of the reductant-containing solution (ii) of a temperature of 25° C., was concentrated with the aid of an ultrafiltration membrane having a molecular weight cut-off of 10,000 (Microza by Asahi Kasei Chemicals Corporation) and washed with a pure water, thereby obtaining a 0.1% by mass alloy particle dispersion liquid with pure water being a dispersion medium thereof (average particle size D₅₀ 60 nm, ratio of antimicrobial metals in alloy particles 100% by mass).

Preparation of Photocatalyst Coating Liquid C

The titanium oxide particle dispersion liquid A and the silicon compound-containing liquid were mixed together so that a ratio of titanium oxide: silicon compound would be 1:1 (mass ratio). A mixed solvent of water/isopropyl alcohol (weight ratio 6/4), as a dispersion medium, was then added and mixed into such mixed liquid in a way such that a concentration of the titanium oxide and silicon compound would be 0.5% by mass, thereby obtaining a silicon compound-containing titanium oxide particle dispersion liquid.

An acetylene-based surfactant (OLFINE EXP 4200, HLB 10 to 13 by Nissin Chemical Industry Co., Ltd.) was then added and mixed into such dispersion liquid by an amount of 0.02% by mass in terms of liquid weight ratio, thereby obtaining a photocatalyst coating liquid C.

Preparation of Photocatalyst Coating Liquid D

The titanium oxide particle dispersion liquid B and the silicon compound-containing liquid were mixed together so that a ratio of titanium oxide: silicon compound would be 1:1 (mass ratio). A mixed solvent of water/isopropyl alcohol (weight ratio 6/4), as a dispersion medium, was then added and mixed into such mixed liquid in a way such that a concentration of the titanium oxide and silicon compound would be 0.5% by mass, thereby obtaining a silicon compound-containing titanium oxide particle dispersion liquid.

An acetylene-based surfactant (OLFINE EXP 4200, HLB 10 to 13 by Nissin Chemical Industry Co., Ltd.) was then added and mixed into such dispersion liquid by an amount of 0.03% by mass in terms of liquid weight ratio, thereby obtaining a photocatalyst coating liquid D.

Preparation of Photocatalyst Coating Liquid E

A photocatalyst coating liquid E was obtained in a similar manner as the preparation of the photocatalyst coating liquid D, except that the silver-copper alloy particle dispersion liquid was mixed thereinto so that a mass ratio of titanium oxide particle/silver-copper alloy particle would be 800.

Preparation of Photocatalyst Coating Liquid F

A photocatalyst coating liquid F was obtained in a similar manner as the preparation of the photocatalyst coating liquid D, except that the concentration of the titanium oxide and silicon compound was set to be 0.7% by mass.

Preparation of Photocatalyst Coating Liquid G (for Comparative Example)

A photocatalyst coating liquid G for comparative example was obtained in a similar manner as the preparation of the photocatalyst coating liquid C, except that the acetylene-based surfactant was not added.

Working Example 1

The photocatalyst coating liquid C was applied to a biaxially oriented polypropylene film as a base film (TORAYFAN 2500H by Toray Industries, Inc., 60 μm) via wire bar coating, followed by performing drying in a dryer at 90° C. for 10 min so as to remove water and isopropyl alcohol, thereby obtaining a photocatalyst transfer film having a photocatalyst layer with a thickness of 50 nm.

Next, in order to evaluate transferability, a laminating roller was used to laminate the photocatalyst transfer film on a PET film as the transfer base material (A4300 by TOYOBO CO., LTD.) under a condition of 160° C., 1 m/min, and in a manner such that the photocatalyst layer would come into contact with the PET film as the transfer base material. The OPP film as the base film of the photocatalyst transfer film was then peeled away, thus obtaining a transfer base material PET film with the photocatalyst layer being transferred thereto (evaluation sample).

The obtained transfer base material to which the photocatalyst layer had been transferred and the OPP film that had been peeled away after transfer were then subjected to various evaluations, and the results thereof are shown in Table 1.

Working Example 2

An evaluation sample was produced and then subjected to various evaluations in a similar manner as the working example 1, except that a PET film (S10 by Toray Industries, Inc.) was used as the transfer base material.

Working Example 3

An evaluation sample was produced and then subjected to various evaluations in a similar manner as the working example 1, except that a melamine resin board was used as the transfer base material.

Working Example 4

An evaluation sample was produced and then subjected to various evaluations in a similar manner as the working example 1, except that an acrylic resin film (by Mitsubishi Chemical Corporation) was used as the transfer base material, and a laminating temperature at the time of performing transfer processing was set to be 140° C.

Working Example 5

An evaluation sample was produced and then subjected to various evaluations in a similar manner as the working example 1, except that the photocatalyst coating liquid D was used as the coating liquid.

Working Example 6

An evaluation sample was produced and then subjected to various evaluations in a similar manner as the working example 1, except that the photocatalyst coating liquid E was used as the coating liquid.

Working Example 7

A photocatalyst transfer film with a 90 nm-thick photocatalyst layer being laminated thereon was produced in a similar manner as the working example 1, except that the photocatalyst coating liquid F was used as the coating liquid; and an evaluation sample was then produced in a similar manner as the working example 1. The evaluation sample was then subjected to various evaluations in a similar manner as the working example 1 as well.

Working Example 8

The silicon compound-containing liquid was further applied to the photocatalyst layer of the photocatalyst transfer film produced in the working example 5 via wire bar coating, followed by performing drying in a dryer at 90° C. for 10 min so as to remove water, thereby obtaining a photocatalyst transfer film with a 50 nm-thick protective layer of the silicon compound being laminated on the photocatalyst layer. An evaluation sample was then produced and subjected to various evaluations in a similar manner as the working example 1.

Comparative Example 1

An evaluation sample was produced and then subjected to various evaluations in a similar manner as the working example 1, except that a PET film was used as the base film.

Comparative Example 2

Attempts were made to produce a photocatalyst transfer film in a similar manner as the working example 1 except that the surfactant-free photocatalyst coating liquid G was used as the coating liquid. However, an evaluation sample failed to be obtained as liquid puddles occurred at the time of drying, the coating film exhibited white turbidity, and an ununiform film was formed.

Comparative Example 3

Attempts were made to produce a photocatalyst transfer film in a similar manner as the working example 1 except that a CPP (cast polypropylene) film was used as the base film. However, an evaluation sample failed to be obtained as liquid puddles occurred immediately after coating was finished, and an ununiform film was formed accordingly.

TABLE 1 Working Working Working Working Working Working example 1 example 2 example 3 example 4 example 5 example 6 Base Type OPP OPP OPP OPP OPP OPP film Ra [μm] 0.49 0.49 0.49 0.49 0.49 0.49 Surface treatment Untreated Untreated Untreated Untreated Untreated Untreated Photocatalyst coating liquid C C C C D E Transfer condition (lamination) 160° C. 160° C. 160° C. 140° C. 160° C. 160° C. 1 m/min 1 m/min 1 m/min 1 m/min 1 m/min 1 m/min Transfer base material PET PET Melamine Acrylic PET PET Film Film resin resin Film Film (A4300) (S10) board film (A4300) (A4300) Elemental Transfer base Ti ∘ ∘ ∘ ∘ ∘ ∘ analysis material side Si ∘ ∘ ∘ ∘ ∘ ∘ Base film side Ti — — — — — — Si — — — — — — Water contact angle [degree] 15 25 25 30 25 25 Appearance Transfer base material side ∘ ∘ ∘ ∘ ∘ ∘ Base film side ∘ ∘ ∘ ∘ ∘ ∘ Working Working Comparative Comparative Comparative example 7 example 8 example 1 example 2 example 3 Base Type OPP OPP PET OPP CPP film Ra [μm] 0.49 0.49 1.76 0.49 0.69 Surface treatment Untreated Untreated Untreated Untreated Untreated Photocatalyst coating liquid F D C G C Transfer condition (lamination) 160° C. 160° C. 160° C. 1 m/min 1 m/min 1 m/min Transfer base material PET PET PET Film Film Film (A4300) (A4300) (A4300) Elemental Transfer base Ti ∘ ∘ ∘ Photocatalyst Photocatalyst analysis material side Si ∘ ∘ ∘ transfer film transfer film Base film side Ti — — — failed to be failed to be Si — — — obtained as obtained as Water contact angle [degree] 25 20 50 uniform film uniform film Appearance Transfer base material side ∘ ∘ ∘ failed to be failed to be Base film side ∘ ∘ x formed. formed.

As is clear from the comparative example 1, when a PET film was used as the base film, although the transfer of the photocatalyst layer (thin film) in and of itself was possible, the photocatalyst layer failed to be transferred to the base material while maintaining the photocatalytic function as the photocatalytic effect was not exhibited due to a large water contact angle, and a poor appearance was also observed on the base film side. Further, it also became clear from each of the comparative examples 2 and 3 that it was difficult to form a uniform film when using a surfactant-free coating liquid and when using a CPP film as the base film.

Meanwhile, as is clear from the working examples 1 to 8, the photocatalyst transfer film having, on the OPP film, the photocatalyst layer formed of the coating liquid containing the titanium oxide particle-containing photocatalyst, silicon compound and surfactant, has a favorable transfer processability with respect to various base materials, and allows there to be transferred a photocatalyst layer exhibiting a high transparency and thus a superior design property even after transfer. 

1. A photocatalyst transfer film having, on a biaxially oriented polypropylene film, a photocatalyst layer containing a titanium oxide particle-containing photocatalyst, a silicon compound and a surfactant.
 2. The photocatalyst transfer film according to claim 1, wherein the silicon compound is a hydrolysis condensate of a tetrafunctional silicon compound, the hydrolysis condensate being obtained under the presence of an organic ammonium salt.
 3. The photocatalyst transfer film according to claim 1, wherein the surfactant is an acetylene-based surfactant.
 4. The photocatalyst transfer film according to claim 1, wherein the photocatalyst layer has a thickness of 20 to 300 nm.
 5. The photocatalyst transfer film according to claim 1, wherein the biaxially oriented polypropylene film has a thickness of 12.5 to 100 μm.
 6. The photocatalyst transfer film according to claim 1, wherein a protective layer containing a silicon compound is further laminated on the photocatalyst layer.
 7. A method for producing a photocatalyst transfer film, comprising: applying a photocatalyst coating liquid to a biaxially oriented polypropylene film, the photocatalyst coating liquid containing a titanium oxide particle-containing photocatalyst, a silicon compound, a surfactant and an aqueous dispersion medium; and performing drying. 